Process of heat treatment of steel.



FEDERICO GIOLITTI, OF TUB/III, ITALY, ASSIGNOR TO SOCIETA ANONIMA ITALIANA GIO,

ANSALDO & (3., OF GENOA, ITALY.

PROCESS OF HEAT TBEATMENTOF STEEL.

No Drawing.

To all whom it may concern:

Be it known that I, Fnnnnrco Gronrr'rr, a

subject of the King of Italy, residin at No.

7 5 Stradale Moncalieri, in Turin, Ita y, have invented certain new and useful Improvements in Processes of Heat Treatment of Steel, of which the following is a specification.

This invention relates to an improved heat treatment in the manufacture of any article of ingot or wrought'steel and especially of 11 parts and armor plates.

The ob] ect of this invention is to diminish the brittleness of the material while increasing its strength and elongation under tensile stress, and its tenacity (that is, its power to resist. shock).

The improved heattreatment is differentiated essentially from the other treatments proposed hitherto, by the fact that in the known treatments the heating before hardening is effected at a single temperature, the value of which is determined by the latest point of transformation of the steel, whereas according to the resent improved process the heating for the ardening is efiected successively at two different strictly determined temperatures, the passage from the first temperature to the second temperature being gradually effected.

The temperatures above referred to are determined as follows:

1. The first temperature is comprised in the interval in which the diffusion phenomena of the different components in the struc-' tural elements of the steel occur with the greatest rapidity, without injuriously affecting the strength of the steel.

The steel under treatment must therefore be heated to a temperature which is at least 100 (lhigher than the third transformation point on heating of the steel in question.

As is well known, the said interval varies in amplitude and position according to the composition of the steel; but itcan be surely and easily determined by means of mechanical or micrographic tests or thermic analysis.

2. The second temperature is 30 C. lower at least than the one which is employed for producin the ordinary homogeneous. tem per. Thls second temperature 1s slightly Specification of. I.etters'Patent. Patented DIar, 11,1919,

A nc tionmed October 14, 1914. Serial No. 866,702.

treated steel, but it is necessary in practice to exceed this limit, more or less, according to the shape and dimensions of themanufactured articles and their composition.

An example of the mode of application of the improved treatment is the following: The article to be treated (which may consist either of a rough rolled or rough wrought or a previously heat treated material) is first gradually heated in a suitable furnace until the entire mass of the article has reached the aforesaid first temperature. This first temperature is maintained constant during an interval of time, experimentally determined, which may vary between very large limits according to the properties of the steel and the shape and the dimensions of the treated articles. For a semi-hard carbon steel this interval may vary from one hour or less for pieces of 2-3 kg. or less to 20 hours or more for ieces of 10 tons or more.

T e temperature of the furnace is next gradually changed to the aforesaid second perature or first heating. The article is then quenched in cold or warm water or in oil, or is hardened by sprinkling. This treatment is generally followed by one of the ordinary tempering 0r re-heating (annealing)- processes when a material with high tenacity and elongation is desired; or it may be followed by one of the well known tempering or hardening processes if it is intended to produce a material having a high degree of hardnesspol b one of the o'rdinary processes for pro ucing a negative hardness (softening) of the articles having a heterogeneous com osition, which results partly in a hard an artly in a tenacious texture of the article a ter treatment.

To give a practical example for the treatment of a determined object formed of a determined steel we are now going to describe the following case cut application is a cylinder having a diameter of'50 centimeters and a length of 6 meters, made of cast steel of the following com- The third transformationpointon heating of a steel of this composition is in the neighborhood of, 900 0., while the corresponding point on the cooling curve is between 580'600 C.

From the tests made it appears that thebest thermical treatment for this steel according to the principles of the processes subject-matter of the present application is the following one (1) Slow heating during about 18 hours.

' up to a uniform temperature of 1070 C. throughout the whole mass of the piece.

(2) Maintaining the above said temperature of 1070 C. for six hours.

(3) Slowcooling (during about six hours) down to a uniform temperature of 680 C. v (4:) Maintaining the above temperature of680 C. for about six hours.

Quenching in oil at ordinary temperature. 7

I With a steel containing the constituents referred to in the proportions given below,

the region in which the diffusion phenomena.

occur with the greatest rapidity on heating will be found to be between 980 and 1050 0.,

and on cooling, inthe neighborhood of 700750 C Carbon ;'i; o. 40

Manganese 0.60 Silicon 0.15 Sulfur--- 0.009% Phosphorus 0.02 Chromium 2.20 Nickel 2.50

. A steel article, for example, a connecting an interval of 2 hours.

(c) Quenched in water from a temperature of 800 C.

\Vith a carbon steel containing the constituentls specified below in the proportion set fort I Carbon 0.45 Manganese 0. 52 Silicon 0.10 Sulfur 0.05 Phosphorus 0.004%

the treatment would be effected as follows (1) Heating gradually to a temperature of about 900 C.-

'(2) Maintainingthe steel at this temperature for from Q'to 12 hours.

(3) Slow cooling to about 800 C.

' (4:) Maintaining the steel at this temperature for a period .equ'al to one-half that stated under (1).

(5) Hardening in warm water or oil at the ordinary temperature. a

(6) If necessary, tempering to obtain the desired tensile strength.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is The process of heat treatment of steel which comprises heating the steel to a temperature .in the neighborhood of that at which the diffusion phenomena of the different components of the steel take place with the greatest rapidity, that is to say at least 100 C. higher than the third transforma tion point on heating of the steel under treatment, then, lowering its temperature to at least 30 C. below the temperature necessary for effecting the ordinary uniform hardening and therefore at least about 50 C. above the critical point Ar In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

' FEDERICO GIOLITTI' Witnesses: I

GIAcoMo CARnAnA, v A. Bonaomo. 

